How do you solve a problem like the whitefly?
THE GARDEN FANATIC
“Shoo fly, don’t bother me!”
-- TRADITIONAL SONG
“Do not use a hatchet to remove a fly from your friend’s
forehead.”
-- CHINESE PROVERB
Last weekend, while shopping for furniture with Catharine, scores
of giant whitefly whizzed by our heads. Their flight formation
resembled a squadron of MIGs -- CC thought they looked more like a
swarm of giant whitefly. Several times larger than the common
whitefly, these unwelcome pests have established themselves in Laguna
and other locales, threatening many species of plants.
Giant whitefly is a winged insect that is found mainly on the
undersides of leaves. When it is disturbed, it will flutter rapidly
around its host plant. All whiteflies belong to a family of insects
called Aleyrodidae, which means flourlike, in reference to the white
coating on their wings. The recent warmer temperatures encouraged the
population of giant whitefly to swell to tremendous numbers sending
gardeners down to their favorite nursery, rather than the beach, in
search of relief.
Hibiscus was originally the host of choice, but the giant whitefly
now attacks a number of plants -- a reported 39 genera at the
beginning of summer. Known Laguna hosts include bird of paradise,
citrus, fuchsia, morning glory, salvia, schefflera and xylosma, among
many others. Adult female whiteflies lay their eggs in a
characteristic circular pattern on the undersides of leaves. The
larvae that hatch from the eggs insert their mouthparts to remove sap
from leaves, weakening plants and causing them to grow poorly.
The giant whitefly eggs, larvae and adults form dense colonies on
the undersides of leaves. Trademark beardlike threads up to four
inches long hang from infested leaves. Because the insects are
actively secreting honeydew, sticky strands of material become a
nuisance, along with the black sooty mold that grows on the
excretions. I have found myself batting and muttering at individual
whiteflies as I bring in the morning paper.
The giant whitefly is resistant to chemical treatment, so those
who believe in elimination through the use of stronger pesticides
will discover that this is not an effective option. The giant
whitefly will simply return, stronger and more pervasive. It is too
widespread and breeds far too quickly for agricultural officials to
be able to eradicate it at this point. The proverbial pesticidal fly
swatter will not eliminate giant whitefly from the landscape.
Many gardeners have discovered that washing off the undersides of
foliage with water can reduce infestations. Although this is my
favored control, it is fair to say that there are limitations. Even
with the most focused attention to forceful spraying, water will only
remove a portion of the whiteflies and provides no residual activity.
I find that infested plants must be washed once or twice (or more) a
week to keep whitefly populations from increasing. The use of
whitefly sticky traps, placed adjacent to host plants, also aid in
slowing the pest down.
If you don’t have time to wash your plants everyday, both
insecticidal soaps and horticultural oils will kill adult whiteflies
and immature larvae through suffocation -- although they are not
particularly effective against eggs and mature larvae. Because these
chemicals have little residual activity, they are not as harmful to
beneficial insects as stronger and more persistent pesticides;
however, they must be applied weekly for control. Thorough coverage
of the undersides of leaves is essential.
We heard Oliver’s insistent mewing as Catharine and I made our way
home. He greeted us with a nod of his head and then raised his paw in
the opposite direction. He had caught his first mouse in years! I
picked up our cat and thought it be nice if he learns to catch
whitefly next. See you next time.
* STEVE KAWARATANI is the owner of Landscapes by Laguna Nursery,
1540 S. Coast Highway in Laguna Beach. He is married to local artist,
Catharine Cooper, and has three cats. He can be reached at (949) 497
2438, or e-mail to landscapes@ln.coxatwork.com.
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